Method for testing blasting machines



Jan. 5 1926. 1,568,609

D; M. M FARLAND METHOD FOR TESTING BLAS'IING MACHINES Filed Nov. 7, 1924 wueuto flawed 272. ifi farland Patented Jan. 5, 1923,

UNITED STATES PATENT OFFi-CE.

DAVID M.

arcrentann, wns'r EETER, PENNSYLVANIA, ASSIGNOR TO ATLAS POWDER COMPANY, OF WILBI; (T913, DELAEHABJE, A CORPORATION OF DELA- VJABE.

ME'II-IGD FOR TESTING- BLASTING MACHINES.

Application filed November To all whom it may concern:

Be it known that DAVID M. MGFARLAND, :itizen of the United States, residing at Vest Chester, in the county of Chester and State of Pennsylvania, has invented certain new and useful Improvements in Methods for Testing Blasting Machines, of which the following is a specification.

My invention relates to improvements in devices used to determine the capacity of electrical blasting machines. The object of the invention is to render it possible to provide any desired factor of safety in the rating of a blasting machine.

It is common practice to detonate high explosives by the use of electric blasting caps. These electric blasting caps are detonated by passing a current of electricity through a resistance wire, or bridge inside the cap. The bridge heats up when an electric current is passed through it. The hot bridge ignites some combustible, readily ignited substance in the cap, causing it to detonate. It is necessary to heat the bridge to a. temperature sufficiently high to ignite the mixture in the cap.

A certain minimum of electric current is required to fire a given kind of electric blasting cap. In order to make sure that the cap will fire, an excess of electrical current should be applied.

It is common practice to rate electrical blasting machines by the number of caps connected in series, which the machine can fire. This number can be determined by connecting various numbers of caps in series, and attempting to explode the caps with a blasting machine.

The above method is time consuming and wasteful of caps. It has been the practice in the past, to substitute for all but one cap in the series, a resistance equivalent to that of all but one of the caps in the series If the one cap used inseries with the resistance fires, it is assumed that the blasting machine can actually fire the number of caps equivalent to the resistance, plus one cap. This method gives the blasting machine an insufiicient factor of safety, and at times, a blasting machine will not actually fire the number of caps indicated by this test.

According to my invention, I connect a fixed resistance in parallel with the one '7, 1924:. Serial No. 748,378.

blasting cap used for the test. By adjusting the value of the fixed resistance which is shunted about the cap, any factor of safety may be secured. If the resistance of the shunt is equal to that of the cap, then half the current will flow through the resist ance, and half through the cap. If the current is sufiicient to fire the cap, then we know that the blasting machine is furnishing twice the amount of current necessary to fire a single electric blasting cap through an added resistance used in series equivalent to that of the number of electric blasting caps for which it is desired to test the machine. For successful series firing it is necessary to have at least twice the current which will fire a single electric blasting cap.

1 do not wish to limit myself to the method of varying the amount of resistance which is connected in series with the test cap and the blasting machine. My invention relates to the use of a fixed resistance connected in parallel with the test cap, and 1n series with a variable resistance. In the accompanying diagrammatic drawing, 5 designates the blasting machine, the capacity of which is to be tested. The terminals 6 and 7 of this machine are connected by conductors 8 and 9 to the terminals 10 and 11 of the testing instrument. The latter comprises a circuit in which a variable resistance 12 and a fixed resistance are included. A blasting cap 14 is connected by wires 15 and 16 to the terminals of the fixed resistance.

If it. be desired to test the blasting machine to determine, for example, whether it has sufficient capacity to fire sixty electric 'lasting caps, the variable resistance 12 is adjusted until it is equivalent to the resistance of fifty-nine electric blasting caps and the lead wires of the blasting cap 1a are connected to the ends of the fixed resistance 13. When the blasting machine 5 is operated the current will pass through conductor 8; that portion of the variable resistance indicated at 12 and conductor 17. Then part of the current will go through the resistance 13 and part through the blasting cap circuit 15, 14 and 16 and back to the blasting machine through conductor 9. 1f the resistance of the shunt 13 is made equal to that of the cap circuit 15, 1 k and 16, equal amounts of current will go through the fixed resistance and the cap circuit.

By making the resistance 13 of some other value than that stated, the ratio of the current passing through the cap circuit to that passing through the fixed resistance, can be changed.

It is to be understood that the invention is not limited to the precise arrangement set forth but that it includes within its purview unatever changes fairly come within either the terms or the spirit of the appended claim.

Having described my invention what I claim is:

The herein described method of testing and rating blasting machines which consists of arranging a variable resistance and a blasting cap in series with the blasting machine and shunting a fixed resistance of 20 determined value across a portion of the circuit which includes only the blasting cap.

In testimony whereof he afiixes his signature.

DAVID M. MoFARLAND. 

